Abstract

In recent years, it has been shown that humans have active brown adipose tissue (BAT) depots, raising the question of whether activation and recruitment of BAT can be a target to counterbalance the current obesity pandemic. Here, we show that a 10-day cold acclimation protocol in humans increases BAT activity in parallel with an increase in nonshivering thermogenesis (NST). No sex differences in BAT presence and activity were found either before or after cold acclimation. Respiration measurements in permeabilized fibers and isolated mitochondria revealed no significant contribution of skeletal muscle mitochondrial uncoupling to the increased NST. Based on cell-specific markers and on uncoupling protein-1 (characteristic of both BAT and beige/brite cells), this study did not show “browning” of abdominal subcutaneous white adipose tissue upon cold acclimation. The observed physiological acclimation is in line with the subjective changes in temperature sensation; upon cold acclimation, the subjects judged the environment warmer, felt more comfortable in the cold, and reported less shivering. The combined results suggest that a variable indoor environment with frequent cold exposures might be an acceptable and economic manner to increase energy expenditure and may contribute to counteracting the current obesity epidemic.

Figure 3

A higher sensation and thermal comfort and lower self-reported shivering were reported on day 10 as compared with day 3. The iAUC decreased with 57%, 72%, and 61% for sensation, thermal comfort, and self-reported shivering respectively (P < 0.05; P < 0.01; P < 0.01, respectively). This was tested with a paired-samples t test. Values are expressed as means with SEM. Black squares represent the third day of acclimation (first time 6 hours cold exposure); white squares represent the tenth day.